1. Technical Field
The present invention relates to a medium transporting roller, which carries out transporting of a recording medium such as paper in a recording device represented by a facsimile, a printer or the like, and a recording device provided with the medium transporting roller.
2. Related Art
In a recording device represented by a facsimile, a printer or the like, a transporting unit which transports a recording medium is provided in an upstream side of the recording unit which performs recording on a recording medium. As a configuration of a transporting unit, there is a transport belt and the like which transport while applying suction to a recording medium, but a configuration using a pair of rollers, which rotate while pinching a recording medium, is typical.
Furthermore, as a configuration of a roller, there is an elastic roller and the like which are formed from rubber or the like, but in ink jet printers in particular, a roller with a shaft shape is used where a high friction layer is formed on a surface of a metallic shaft as shown in JP-A-2001-63862 and JP-A-2001-158544. Here, the high friction layer is formed by holding abrasion resistant particles on an outer circumference surface of the shaft body using an adhesive layer and performs a function of improving a friction coefficient with the recording medium and preventing slipping.
In a case of using a roller with a shaft shape as a medium transporting roller, it is possible to select a solid shaft or a hollow (cylindrical) shaft. While rigidity is high and transport precision is high, a solid shaft results in higher costs and an increase in weight of the device. In regard to this, it is possible for a cylindrical shaft to contribute to reducing the weight of the device and lowering the cost.
Furthermore, the present applicants have proposed a cylindrical shaft structure shown in JP-A-2006-289496 as a structure of a cylindrical shaft. The cylindrical shaft described in JP-A-2006-289496 is a cylindrical shaft formed using a metallic plate material where a pair of opposing end portions has been joined, but a structure of a joining portion is configured as a shape with concavities and convexities (referred to in the specifications below as a “zigzag shape”), and according to this, mechanical joining strength is improved. Furthermore, the concavities and convexities which configure the zigzag shape are not simply concavities and convexities but are configured to join up similar to pieces in a so-called jigsaw puzzle by convexities where the width gets wider toward a top end and concavities which engage with the convexities so as to not easily separate when engaged.
However, while contributing to improving mechanical strength of the roller, the joining portion formed in the jigsaw shape has a negative effect in that it is easy for a front edge of a recording medium to get caught up when transporting the recording medium.